Young boys with Fragile X Syndrome were characterized on the basis of a range of physical characteristics. Results were compared with a group of developmentally delayed boys of similar age who were known to test negative for Fragile X. The results of this study underscored the difficulty of identifying Fragile X Syndrome on the basis of physical characteristics: although it confirmed a number of reported profiles, it also underscored the considerable overlap in the two populations. Findings of this study differed from certain other reports in the lack of significantly greater incidence of ear infections. A major result of these investigations was the identification of significantly enlarged testicular volume in young boys with Fragile X syndrome, and its characterization and relationship with age. Lachiewicz AM, Dawson DV, Spiridigliozzi GA. Physical characteristics of young boys with Fragile X syndrome - Exploring the difficulty of making a clinical diagnosis in young males. Future work will focus on behavioral aspects.